Composite reinforcer (R-2) self-adhesive, by curing, to a diene rubber matrix, which can be used as reinforcing element for a tire, comprising: one or more reinforcing thread(s) (20), for example a carbon steel cord; a first layer (21) of a thermoplastic polymer, the glass transition temperature of which is positive, for example, a polyamide 6,6, covering individually said thread or each thread or collectively several threads; a second layer (22) comprising a functionalized diene elastomer bearing functional groups selected from epoxide, carboxyl, acid anhydride and acid ester groups, for example, an epoxidized natural rubber, covering the first layer (21). Process for manufacturing such a composite reinforcer and rubber article or semi-finished product, especially a tire, incorporating such a composite reinforcer.